Transcript Biological Basis of Memory

BIOLOGICAL BASIS OF
MEMORY
Biological Basis of Memory
Karl Lashley searched for a localized memory trace
or engram
Believed that memory was
localized – specific memory stored
in a specific area.
Removed parts of rat’s cerebral
cortex but found no one area
contained the memory of the maze
Found that maze-learning in rats
was distributed throughout the
brain
Memory and the Brain
• Play “The Locus of Learning and
Memory” (6:28) Module #16 from The
Brain: Teaching Modules (2nd edition).
• Watch first 3 minutes on Lashley’s
Experiment and if time view Penfield’s
experiment & why it was flawed.
Biological Basis of Memory
Richard Thompson
Reflexive Behaviors are
localized in the cerebellum
• Thought that cerebellum
was changed after
classically conditioning a
rabbit to blink to a tone.
He was right!
• Removing this area
caused the rabbit to no
longer blink to a tone but
only reflexively. Shows
localized memory.
• This did not work for
complex behaviors like
running a maze, which
seem to be distributed
Biological Basis of Memory
• fMRI shows that when people memorized the label
“dog” with the sound of a bark the auditory cortex
activated when they retrieved it.
• Those memorized the label “dog” to a picture
activated their visual cortex when they retrieved it.
• Retrieving a memory reactivates the sensory area
of the cortex that was involved in the initial
perception of the event. (See images on pg. 268)
New Memories in a Snail
• Aplysia—a sea
snail was used
to study how
memories can
change
neurons
Eric Kandel
Kandel’s Sea Snail Experiment
• Eric Kandel – studied neural changes that took place
in Aplysia, a sea snail. Click HERE to view it (4 min)
• Squirted it with water followed by an electric shock
that classically conditioned it to withdrawal its gills
next time it was squirted.
• This changed the three neuron circuit in the snail.
• Function of the neuron changed with increase in the
amount of the neurotransmitter produced by the
neuron.
• Structure of the neuron changed with the number of
interconnecting dendrites and axon terminals
increasing allowing for more communication points
(synapses).
Long-Term Potentiation
• Two possible changes should occur in the
neurons in forming memories.
1. Functioning of neurons in the brain could change
2. Structure of the neurons could change.
• These increase the neuron’s firing potential
• Kandel’s experiment shows this.
• Believed to be the neural basis of learning
and memory
Severe Memory Loss
• Amnesia—severe memory loss
3 Major Types:
1. Retrograde Amnesia
2. Anterograde Amnesia
3. Infantile Amnesia
Retrograde amnesia
• Retrograde amnesia—inability to remember PAST
episodic information; common after head injury;
Reason for this is it may disrupt:
– Memory Consolidation – gradual, physical process of
converting a long-term memory to a stable and
enduring memory code.
– If disturbed before the process is complete, memory
could be lost.
– Sleep seems to be when most memory consolidation
occurs
Anterograde amnesia
• Anterograde amnesia—inability to form NEW
memories; related to hippocampus damage
– Shows that hippocampus must be used in the
encoding of new memories and transferring them
from STM to LTM.
– Implicit memories like procedural memories do still
occur showing that these may not involve the
hippocampus but knowing they are there (explicit
memory) does not work showing the hippocampus is
involved in these.
Infantile Amnesia
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Infantile Amnesia – Inability to recall events from
the first few years of life.
Possible Reasons for this:
1. Too many differences between the world of an infant
and ours for us to be able to make connections or
retrieval cues to retrieve them (encoding specificity
principle).
2. Hippocampus is still developing so they cannot form
new LTM but they can make procedural memories.
3. One reason adults typically recall little of their first
three years of life is that during infancy they were
unable to verbally label most of their experiences
(semantically encode the info).
Brain Structures Involved in Memory
Emotions & the Amygdala
• Amygdala may help in formation of emotional
memories.
• Watch Enhancing Memory (7:50) to see how
research is showing this. Click below.
Evidence for Separate
Implicit/Explicit Systems
• Neurophysiological evidence
• Patient H.M. (Henry Gustav Molaison)
– life-threatening seizures originating in temporal lobe
– surgically removed portions of temporal lobe
Temporal Lobe
• Includes:
– hippocampus
– Amygdala
• Verbal
information is
stored in the left
hippocampus and
• Visual designs
are stored in the
right
hippocampus
Patient H.M.
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Click HERE for a video on H.M. (10 Min)
Surgery was effective in reducing seizures
BUT, had other side effects as well
Can remember explicit memories acquired before
the surgery
– e.g., old addresses, normal vocabulary
• Cannot form NEW explicit memories
– e.g., remembering the name of someone he met 30
minutes prior
– cannot name new world leaders or performers
– can recognize a picture of himself from before his
surgery but not from after and doesn’t recognize
himself in a mirror
Patient H.M.
• H.M. has severe explicit / declarative memory
disorder
• H.M. is almost normal on procedural or implicit
memory tasks including priming, classical
conditioning, and learning motor skills
• When given the same logical puzzle to solve for
several days in a row, H. M. was able to solve the
puzzle more quickly each day.
• This shows that explicit memory depends upon the
temporal lobes and implicit does not
Patient H.M. Summary
• Temporal lobe damage led to deficits in explicit,
but not implicit memory
– H.M. had both episodic and semantic memory deficits
• Damage to the hippocampus alone produces
episodic, but not semantic memory deficits
• Why did H.M. show both types of explicit
memory deficits?
– He had damage not only to hippocampus, but to other
structures as well
Memory and the Hippocampus
• Damage to the hippocampus would
result in the inability to form new
explicit memories, but the ability to
remember the skills of implicit
memories
•To view someone
with this damage
checkout the video
by clicking on it
(7:38)
Memory and the Hippocampus
Hippocampus and Memory
• Play “Living with Amnesia: The
Hippocampus and Memory” (10:35)
Module #18 from The Brain:
Teaching Modules (2nd edition).
• Watch if Time Allows.
Aging and Memory
• Studies have found that the ability to recall
new information, unaided by clues,
declines with age,
• But the ability to recognize new
information, as in a multiple-choice
question, does not.
• Elderly may need more time to retrieve
memories but still can do as well as a
young person.
Culture & Memory
• Levy and Langer study of cultural views of
aging show that society’s expectation that
older people will have poorer memories can
be a self-fulfilling prophecy.
• In cultures where that is not believed (Asia)
the elderly show memories just as good as
the young.
Think your memory is something special?